Photoelectric cell circuit



Feb. 25, 1936.

W. N. GOODWIN, JR

PHOTOBLECTRIC CELL CIRCUIT Filed June 23, 1935 temperature conditions and is stable.

Patented Feb. 25, 1936 UNITED STATES.

PHOTOELECTRIC CELL CIRCUIT William Nelson Goodwin, Jr., Newark, N. 1., assignor to Weston Electrical Instrument Corporation, Newark, N. 3., a corporation of New Jersey REISSUEB Application June 23, 1933, Serial No. 677,332

8 Claims.

This invention relates to circuits for photoelectric cells of the flat disk or barrier layer type. and more particularly to measuring relay circuits in which the direction and magnitude of current flow are to depend upon a difference in the light intensities at two cells of the barrier layer type.

It has been found impractical to connect current-generating photoelectric cells of the barrier layer type differentially in series opposition, that is, in a single series circuit including two cells an a current responsive device, the circuit connections being such that the voltage generated in one cell directly opposes that generated in the other. This arises from the fact that the voltage and resistance characteristics of these cells are aflected by temperature and other efiects. Since each cell works into the other, the current output of each is not determined solely by the light intensity at that cell but varies with the voltage and resistance of the second cell. On the other hand, the current generated in a relatively low resistance circuit is practically independent of For this reason, each cell must be so connected in a relatively low resistance circuit, and the circuits so arranged that the effects of the currents can be diiierentially combined in opposition.

An object of the invention is to provide a sensitive and stable photoelectric cell circuit including a pair 01' cells of the barrier layer type and a current response member subjected to the differential action oi currents generated by the cells. A further object is to provide a circuit of the type stated, and in which current generated by one cell may flow in a circuit which does not include the other cell. More particularly. an objcct is to provide a relay system including a pair of photoelectric cells or the barrier layer type and a relay, the electrical network of said cells including a common path or branch in which the relay is located and in which the separate cells tend to establish current flow in opposite directions, and other branches which complete a series circuit for each cell.

These and other objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawing, in which:

Fig. 1 is a circuit diagram oi an embodiment of the invention which is appropriate for a determination of the relative illumination of two photoelectric cells;

Fig. 2 is a fragmentary circuit diagram oi a relay circuit embodying the invention; and

Figs. 3 and 4 are circuit diagrams oi measurng systems embodying the invention.

In the drawing, the reference numerals l, 2, identify two photoelectric cells of the direct action or barrier layer type, the cells being usually oi. similar design and operating characteristics. The cells are subjected to illumination from two different sources or to light rays reaching the cells from the same source but by different paths. As represented diagrammatically in the drawing, this condition of unequal illumination may obtain when the cells I, 2 are illuminated by separate light sources 3, 4, respectively, a shield 5 being positliloned to prevent a cross-illumination oi the ce s.

A measuring instrument 6 is a series element in the lead I that connects similar electrodes 8 of the two cells, and the other pair of similar electrodes 8 are joined by a lead Hi. It will be noted that leads I and In complete a series circuit which includes the cells and instrument, the cells being oppositely arranged in the circuit 'and thereby tending to establish current flow in opposite directions.

In accordance with the invention, additional circuit elements are provided to complete relatively independent circuits for each cell. As illustrated, a resistance I I is shunted across the measuring instrument, and an adjustable tap l2 on the resistance is connected to the lead it! through a connection l3. If desired, a scale It may be provided to indicate, on some convenient system of graduations, the setting of the tap l2 along resistance H.

The added circuit elements cooperate with the original series circuit to form a plurality of loop circuits which have portions in common, but in which the cells are in the non-common portions of diiierent loop circuits. When either cell is darkened, the resistance of the loop circuit of that cell is very high, but the loop circuit oi the other cell provides a relatively low resistance path for current flow in accordance with the illumination at the other cell.

The tap I 2 is adjustable over resistance It to balance the current output from the. two cells. but not their output voltages, by regulating the magnitude of the sections oi. resistance H which are included in the two loop circuits. This operation does not involve a comparison of the resistances oi the photocells or a comparison oi the values of the two sections into which resistance II is divided by the tap l2. since the circuit does not have the general form oi and does not function as a Wheatstone bridge. The

electro-motive forces from self-generating cells are balanced against those differences oi potential across resistors which are produced by currents from the respective cells. The circuit elements which divide the main series circuit into loop circuits are passive, l. e., do not include batteries or other sources of current which are essential for Wheatstone bridge operation.

When the system includes a measuring instrument or galvanometer 6, the apparatus may be employed for brilliancy, transmission or opacity measurements, and the substitution of a relay for the instrument permits the automatic operation of mechanism in accordance with variations in these factors.

In the relay system shown in Fig. 2, the general circuit arrangement is, or may be, substantially identical with that of Fig. 1, except that the moving coil it of a relay is connected in lead I, the relay including a contact arm it which is movable between contacts l1, it to close a circuit including a current source l9 and, respectively, the responsive devices 20 or 2|. By adjusting the tap [2 to bring the contact arm I8 into its neutral position when the cells develop equal currents, or currents bearing a predetermined ratio to each other, a departurein either sense from that initial condition of illumination and resulting current flow will result in a deflection of contact arm it towards one or the other oi contacts l1, 18.

The circuit shown in Fig. 3 provides a simple and eillcient instrument arrangement for measuring the relative illumination 0! the photoelectric cells I, 2. Like electrodes 8 of each cell are connected by leads 1' to the separate coils of coil sections of a measuring instrument 6, and the common junction of the coils is connected by lead ii to the Jumper or common lead i0 oi the other pair of like electrodes 0 of the cells. The sections of the instrument coil are so positioned that the deflection oi the pointer varies as the ratio oi the currents generated by the separate cells.

In the similar measuring circuit of Fig. 4, the two sections of the moving coil system are so positioned that currents flowing from the two cells, as indicated by the arrows, exert opposite eiiects upon the motion of the complete coil system, and the resulting deflection is proportional to the diii'erence in the current outputs of the two cells. As with the other forms of the invention, it is to be noted that the path of current flow of each cell does not include the other cell. I

The exact circuit arrangement of networks embodying the invention is subject to some variation, so long as the current responsive device is located in a branch of the network in which current ilow from the two cells tends to establish opposite etiects, and the cells are located in the non-common portion oi two loop circuits which have at least a portion in common.

I claim:

1. In a photoelectric cell circuit, a pair of photoelectric cells of the barrier layer type, a current responsive device, and a network connecting said cells and device to subject said device to the diii'erential action of currents generated by the said cells; said network including a main series circuit comprising circuit elements joining one set 0! like terminals of said cells and connecting the device between the other set oi. like terminals, and means forming a shunt path dividing said main series circuit into two loop circuits having the cells in the non-common portions of the respective loop circuits, said means consisting of passive circuit elements connected between the joined terminals of said cells and said device cells are in the non-common portions of two loop circuits.

2. A photoelectric cell circuit as claimed in c aim 1. wherein said current responsive device comprises a measuring instrument having a moving coil formed in two sections, the respective sections being located in non-common portions of the two loop circuits.

3. In photoelectric apparatus for measuring the diflerence in the illumination at two points. a pair of barrier layer photoelectric cells adapted to be positioned at the said two points, a direct conductive connection between one set of like terminals oi said cells, a current measuring instrument having an operating winding comprising two sections having a terminal in common, circuit elements completing a series circuit including both cells and both sections of said operating winding, and a lead connecting the common terminal 01 said operating winding to said conductive .eonnection, whereby the common terminal of said winding is maintained at the common potential of the set of like cell terminals which are Joined by said conductive connection.

4. In a photoelectric cell circuit, a pair of barrier layer type photoelectric cells, a current responsive device, leads connecting said cells to said device to subject the same to the opposing influence of currents generated by the separate cells, and additional circuit elements 01 passive type forming a path of current flow for each cell which is substantially independent of the other cell.

5. In apparatus of the type stated, a pair of photoelectric cells oi the barrier layer type and each having a pair of electrodes, a current responsive device connected between similar electrodes of said pair of cells, a lead connecting the other electrodes of said cells, a resistance shunting said device, and a passive connection from a point on said resistance to said lead.

6. Apparatus as claimed in claim 5, wherein said connection includes a tap adjustable along said resistance.

7. Apparatus as set forth in claim 5, wherein said device is a current measuring instrument.

8. Apparatus as set iorth in claim 5, wherein said device is a relay, and said relay includes a contact arm movable in response to the diflerence oi the currents generated by said cells, and a contact adapted to be engaged by said contact arm.

WILLIAM NELSON GOODWIN, Jr.

CERTIFICATE or CORRECTION. 5

Patent No. 2,032,010. Fe ruary 25, 1936 WILLIAM NELSON GOODWIN, JR.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, lines 14 and 15, claim 1, strike out the words "cells are in the noncommon portions of two loop circuits"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of April, A. D. 1936.

Leslie Frazer (S Acting Commissioner of Patents.

CERTIFICATE OF CORRECTION. 5

Patent No. 2,032,010. Fe ruary 25, 1936 WILLIAM NELSON GOODWIN, JR.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, second column, 'lines 14 and 15, claim 1, strike out the words "cells are in the noncommon portions of two loop circuits"; and that the said Letters Patent should be read with vthis correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 7th day of April, A. D. 1936.

Leslie Frazer Acting Commissioner of Patents. 

